Study on strain softening model of sandstone based on energy principle

In order to establish the nonlinear damage equation of graded sandstone rock based on the principle of energy,three axial tests were carried on the sandstone under different confining pressure conditions,and the mechanical properties of its peak were analyzed.It was concluded that the increase of confining pressure increases the stress level corresponding to the initial point of sandstone expansion and delayed the non-linear expansion of sandstone.The confining pressure increased the bearing capacity of the rock to a certain extent.At the same time,the brittle failure degree of the rock was weakened and the ductility was increased,so that the sample tended to form a single shear plane.The sample was complete after failure.Under different confining pressures,the stage of the rock peak moved and slided along the fracture surface.It still had some bearing capacity,and the deformation rate of rock decreased gradually.It was assumed that the change rule of stress-strain relationship satisfies cubic polynomial.The nonlinear damage model was established through the energy principle,which could better reflect the relationship and damage of rock stress-strain.Finally,the correctness of the model was verified by comparing the experimental curve with the high fitting degree of the fitting curve.